IC 434 - Horsehead nebula

Dark cloud in the constellation of Orion.

The Horsehead Nebula is a 3 light-years large part of a dark cloud in the constellation Orion, which stands out in front of the red shining emission nebula IC 434 with a silhouette similar to a horse's head.

The nebula is about 1,500 light years away from Earth and therefore appears to be a quarter the size of the Earth Moon.The Horsehead Nebula is an accumulation of cold gas and dust that emit very little light in the visible spectrum and therefore appears dark. This dark area can also be resolved by longer exposure times or with large telescope apertures.Studies in the millimeter and submillimeter range show that the nebula consists predominantly of molecular hydrogen, and that it also contains a large number of different simple hydrocarbon compounds, some with an oxygen and sulfur content. These molecules have a temperature of about 100 Kelvin in the outer area and 15 Kelvin in the core area of the nebula; it has about 27 times the mass of the sun.[15][16] The gas masses move, which is why the nebula will lose its resemblance to a horse's head in a few thousand years.